main() {
  //算术运算符
  double price = 99.99;
  int count = 5;
  double allPrice = price * count;
  print(allPrice);


  int index=0;
  index++;
  ++index;
  print(index);

  if(0 != "0"){
    print("比較正確");
  }

  String defaultValue="默认值";

  if(defaultValue.isEmpty){
    print("111");
  }

}
